Name: ____________________________
Date: _______________
Hour: _____
Naming Ions
To write an ion, you write the symbol of the atom and put the charge in the upper right corner. Consider
the following examples: Al3+, O2-, Mg2+. You should verify that each of the charges is correct.
Positive and negative ions are named differently. Positive ions retain the same name as the parent atom.
For example, Al3+ is called the “aluminum ion” and Mg2+ is called the “magnesium ion.” Negative ions are
named a little differently. For negative ions, you change the ending of the name to “-ide”. Therefore, O2- is
named oxide and P3- is named phosphide.
Questions
1. Write the symbol (including the charge) and name for each of the ions for each of the following:
a) Ca
b) Cl
c) N
d) K
e) S
f) B
g) P
Information: Ionic Bonding and Formulas
There are two ways in which atoms can “bond” to each other and form a compound. The means of bonding that
we will consider now is called ionic bonding, which occurs between a metal and a nonmetal. As you know,
opposite charges attract. Ionic bonding is when two ions of opposite charge attract and bond to each other
forming an ionic compound. Consider the following examples of formulas for ionic compounds:




One Na+ (sodium ion) and one Cl- (chloride ion) bond to make NaCl, “sodium chloride.”
One Mg2+ (magnesium ion) and two F- (fluoride ion) bond to make MgF2, “magnesium fluoride.”
Three Ca2+ (calcium ion) and two N3- (nitride ion) bond to make Ca3N2, “calcium nitride.”
One Al3+ (aluminum ion) and one N3- (nitride ion) bond to make AlN, “aluminum nitride.”
The small numbers at the bottom right of each symbol in a formula are called “subscripts”. Subscripts tell us
how many of each type of atom are present. For example in the formula Mg3N2 there are three magnesium ions
and two nitride ions.
Questions
2. Consider the formula NaCl in the above example. It tells us that one Na+ ion is bonded to one Cl- ion.
What is the overall charge for NaCl? Is it positive, negative, or neutral?
3. Consider MgF2. This formula tells us that one Mg2+ ion bonds with two F- ions. What is the overall charge
on MgF2?
4. What is the overall charge on any ionic compound?
5. The formula Ca3N2 can never be written as N2Ca3. To find out why, take note of each of the four example
formulas given above.
a) In terms of charge, what do the first ions named all have in common?
b) In terms of charge, what do the second ions named all have in common?
c) Now, why can’t Ca3N2 ever be written like N2Ca3?
6. There are two rules to follow when writing formulas for ionic compounds. One has to do with charges and
the other has to do with which atom to write first and which one to write second. What are these two rules?
7. Write the name for the compound that forms when the following atoms form ionic compounds. The first is
done for you.
a) Na3N
b) BaS
c) MgI2
sodium nitride
d) Al2O3
e) Ca3P2
f) Na2S
Polyatomic Ions
The word, “polyatomic” means “many atoms”. A polyatomic ion, therefore, is an ion that is made of more than
one atom. An example of a polyatomic ion is the sulfate ion, SO42-. Sulfate is composed of one sulfur atom
and four oxygen atoms and overall sulfate has a negative two charge.
Some polyatomic ions:
Sulfate: SO42Cyanide: CNAcetate: C2H3O2-
Phosphate: PO43Ammonium: NH4+
Hydroxide: OH-
Nitrate: NO3Chlorate: ClO3Carbonate: CO32-
Questions
1. What do all of the polyatomic ions that have the suffix “-ate” have in common?
2. Which two atoms do you think compose the polyatomic ion called “silicate”?
3. What is the difference between calcium nitride and calcium nitrate?
Writing Formulas With Polyatomic Ions
First of all, you must remember that you can never change the formula for a polyatomic ion. Sulfate is always
SO42- and never S2O84- or something else. Following are some examples of chemical formulas that contain
polyatomic ions.
Ammonium chloride is formed from one ammonium ion (NH4+) and one chloride ion (Cl-) to give the formula:
NH4Cl. Sodium sulfate requires two sodium ions (Na+) because sulfate (SO42-) has a negative two charge; the
formula is: Na2SO4.
Consider calcium hydroxide. Calcium has a positive two charge (Ca2+) and hydroxide has a negative one
charge (OH-). We need two hydroxide ions to combine with one calcium ion so that the overall charge ends up
being zero. We write calcium hydroxide like Ca(OH)2.
Following are some more examples:
potassium acetate: KC2H3O2
barium phosphate: Ba3(PO4)2
magnesium nitrate: Mg(NO3)2
calcium carbonate: CaCO3
Questions
4. As mentioned above, calcium hydroxide is written like Ca(OH)2. Why can’t it be written like CaOH2?
5. As mentioned above, barium phosphate is written as Ba3(PO4)2. Why can’t it be written like Ba3PO42?
6. Name the following compounds. Each includes at least one polyatomic ion.
a) Na3PO4
b) (NH4)2SO4
c) Mg(C2H3O2)2
d) (NH4)2S
e) CaCO3
f) Ba(NO3)2
Charges of Some Transition Elements
So far you have learned that you can predict the charge that an ion will have based on its location on the
periodic table. However, the transition elements are not easy to predict. A few common transition elements are
listed below. You should memorize their charges.
Silver: Ag+
Zinc: Zn2+
Cadmium: Cd2+
More Than One Possible Charge
Many transition elements can have more than one charge when they become an ion. Copper ions, for example,
can be Cu+ or Cu2+. As another example, iron ions are sometimes Fe2+ and sometimes Fe3+.
Questions
1. Copper and iron are in the “d block” and so you need to calculate their charge by comparing what bonds
to them. Find the charge on copper and iron in each of the following compounds.
a) CuCl2
b) CuCl
c) FeSO4
d) Fe2(SO4)3
2. Give your best attempt at naming the compounds from question 2. (They are rewritten below.)
a) CuCl2
b) CuCl
c) FeSO4
d) Fe2(SO4)3
Formulas Containing Roman Numerals
You probably put the same name for the compounds in question 3a and 3b. You may also have put the same
name for the compounds in 3c and 3d. BUT these are not the same compound! You cannot have the same
name for two different compounds. Here are the correct names for the compounds in questions 2 and 3:
a) CuCl2
copper(II) chloride
b) CuCl
copper(I) chloride
c) FeSO4
iron(II) sulfate
d) Fe2(SO4)3
iron(III) sulfate
Questions
3. Compare your answers for questions 2 &3 with the names of the compounds given in the information
section. What do the Roman numerals stand for?
4. Name the following compounds.
a) FeNO3
b) Cu3(PO4)2
c) ZnCl2
d) AgNO3
Covalent
Recall that an ionic bond results from the combination of a metal and a nonmetal. A covalent bond is the type
of bond between two nonmetals. Covalent bonds are formed by neutral atoms that share electrons rather than
by charged ions. When a compound is formed by sharing electrons, the compound is called a molecule or
molecular compound. It is important to note that ionic compounds are not called molecules. The largest class
of molecules are called organic molecules. Carbon is the distinguishing mark of organic compounds.
Questions
1. Circle any of the following compounds that would properly be called a “molecule”.
a) H2O
b) CO2
c) NaCl
d) Mg3P2
e) N2O5
Information: Naming Covalent Compounds
There are several prefixes used to name molecules. The name “carbon oxide” is not sufficient because carbon
and oxygen sometimes form CO2 and sometimes CO. Prefixes are necessary to distinguish between them.
Formula
N2O4
SF6
XeCl5
SO3
CO
Name
dinitrogen tetraoxide
sulfur hexafluoride
xenon pentachloride
sulfur trioxide
carbon monoxide
Questions
2. Fill in the table to indicate which prefix is used to represent the numbers. The first one is done for you.
Number
Prefix
1
mono
2
3
4
5
6
3. Name each of the following molecules using the appropriate prefixes.
a) N2O5
b) CF4
c) SCl3
d) SO